package com.ninetowns.ui.widget.refreshable;

import com.ninetowns.ui.widget.refreshable.PullToRefreshBase.Mode;

import android.annotation.TargetApi;
import android.view.View;


@TargetApi(9)
final class OverscrollHelper {

    static final String LOG_TAG = "OverscrollHelper";
    static final float DEFAULT_OVERSCROLL_SCALE = 1f;

    /**
     * Helper method for Overscrolling that encapsulates all of the necessary
     * function.
     *
     * This should only be used on AdapterView's such as ListView as it just
     * calls through to overScrollBy() with the scrollRange = 0. AdapterView's
     * do not have a scroll range (i.e. getScrollY() doesn't work).
     *
     * @param view
     *            - PullToRefreshView that is calling this.
     * @param deltaY
     *            - Change in Y in pixels, passed through from from overScrollBy
     *            call
     * @param scrollY
     *            - Current Y scroll value in pixels before applying deltaY,
     *            passed through from from overScrollBy call
     * @param isTouchEvent
     *            - true if this scroll operation is the result of a touch
     *            event, passed through from from overScrollBy call
     */
    static void overScrollBy(final PullToRefreshBase<?> view, final int deltaY,
            final int scrollY, final boolean isTouchEvent) {
        overScrollBy(view, deltaY, scrollY, 0, isTouchEvent);
    }

    /**
     * Helper method for Overscrolling that encapsulates all of the necessary
     * function. This version of the call is used for Views that need to specify
     * a Scroll Range but scroll back to it's edge correctly.
     *
     * @param view
     *            - PullToRefreshView that is calling this.
     * @param deltaY
     *            - Change in Y in pixels, passed through from from overScrollBy
     *            call
     * @param scrollY
     *            - Current Y scroll value in pixels before applying deltaY,
     *            passed through from from overScrollBy call
     * @param scrollRange
     *            - Scroll Range of the View, specifically needed for ScrollView
     * @param isTouchEvent
     *            - true if this scroll operation is the result of a touch
     *            event, passed through from from overScrollBy call
     */
    static void overScrollBy(final PullToRefreshBase<?> view, final int deltaY,
            final int scrollY, final int scrollRange, final boolean isTouchEvent) {
        overScrollBy(view, deltaY, scrollY, scrollRange, 0,
                DEFAULT_OVERSCROLL_SCALE, isTouchEvent);
    }

    /**
     * Helper method for Overscrolling that encapsulates all of the necessary
     * function. This is the advanced version of the call.
     *
     * @param view
     *            - PullToRefreshView that is calling this.
     * @param deltaY
     *            - Change in Y in pixels, passed through from from overScrollBy
     *            call
     * @param scrollY
     *            - Current Y scroll value in pixels before applying deltaY,
     *            passed through from from overScrollBy call
     * @param scrollRange
     *            - Scroll Range of the View, specifically needed for ScrollView
     * @param fuzzyThreshold
     *            - Threshold for which the values how fuzzy we should treat the
     *            other values. Needed for WebView as it doesn't always scroll
     *            back to it's edge. 0 = no fuzziness.
     * @param scaleFactor
     *            - Scale Factor for overscroll amount
     * @param isTouchEvent
     *            - true if this scroll operation is the result of a touch
     *            event, passed through from from overScrollBy call
     */
    static void overScrollBy(final PullToRefreshBase<?> view, final int deltaY,
            final int scrollY, final int scrollRange, final int fuzzyThreshold,
            final float scaleFactor, final boolean isTouchEvent) {

        // Check that OverScroll is enabled
        if (view.isPullToRefreshOverScrollEnabled()) {
            final Mode mode = view.getMode();

            // Check that we're not disabled, and the event isn't from touch
            if (mode != Mode.DISABLED && !isTouchEvent && deltaY != 0) {
                final int newY = (deltaY + scrollY);

                if (newY < (0 - fuzzyThreshold)) {
                    // Check the mode supports the overscroll direction, and
                    // then move scroll
                    if (mode.canPullDown()) {
                        view.setHeaderScroll((int) (scaleFactor * (view
                                .getScrollY() + newY)));
                    }
                } else if (newY > (scrollRange + fuzzyThreshold)) {
                    // Check the mode supports the overscroll direction, and
                    // then move scroll
                    if (mode.canPullUp()) {
                        view.setHeaderScroll((int) (scaleFactor * (view
                                .getScrollY() + newY - scrollRange)));
                    }
                } else if (Math.abs(newY) <= fuzzyThreshold
                        || Math.abs(newY - scrollRange) <= fuzzyThreshold) {
                    // Means we've stopped overscrolling, so scroll back to 0
                    view.smoothScrollToLonger(0);
                }
            }
        }
    }

    static boolean isAndroidOverScrollEnabled(View view) {
        return view.getOverScrollMode() != View.OVER_SCROLL_NEVER;
    }
}
